Two-temperature refrigerating system



Dec. 23, 1952 TWO-TEMPERATURE REFRiGERATING SYSTEM Filed Jan. 6, 1950 2 SHEETS-SHEET 1 Fig.1.

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Inventor:

Charles S.Grimshaw,

His Attorney.

Dec. 23, 1952 1-5. RM'Q'H 2,622,405

TWOTEMPERATURE"REFRIGERATING sYsTEII/I Inventor; Charles S. Grimshaw,

by His Attorney.

Patented Dec. 23, .5952

Two-TEMP RATURE BE R GEBAT N SY M Charles S. Grimsha w, Erie, Pan, assignor to General Electric Gompany, a corporation of New York Applicaticn January 6, 1950, Serial Nc.;137; .36

Claims.

.My invention relates to refrigerating systems and, more particularly, to refrigerating systems including two evaporators adapted to operate at different temperatures.

It is an object of my invention to provide a refrigerating system including two evaporators operating at difierent temperatures and including an improved arrangement for operating the system at high efiiciency.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of the specification.

In carrying out the objects of my invention, a low temperature evaporator of the flooded type is arranged in a closed refrigerant circuit with a condensing unit. A higher temperature evaporator is connected to the header of the low temperature evaporator to receive liquid refri erant from the header and to return vaporized refrigerant to the header. The operation of the condensing unit is controlled by'a temperatureresponsive bulb arranged on the header.

For a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. 1 is a schematic diagram'of a refrigerating system illustrating an embodiment of my invention; Fig. 2 is a view of a modified form of a portion of the refrigeratin system illustrated in Fig. 1; Fig. 3 is a view of still another modified form of the portion of the refrigerating system shown in Fig. 2; Fig. 4 is .a graph showing temperatures during one cycle of the condensing unit; and Fig. 5 is a similar graph showing temperatures under different conditions.

Referrin to Fig. 1, the refrigerating system includes a condensing unit I, a low temperature evaporator 2, and a header 3 connected in closed series refrigerant circuit. The condensing unit I includes a condenser 4 and a motor-compressor unit hermetically sealed within a case 5. Liquid refrigerantis supplied from the condensing unit to thelow temperature evaporatorl through a restricted tube 6 and vaporized refrigerant is returned to the condensing unit through a suction line orconduit 1.

The refrigerating system includes -a-second evaporator .8 which is adapted -to eperateat a higher temperature than the low temperature evaporator 2. In application to a refrigerator low temperature evaporator .2 maybe employed, for example, tocool the frozen food compart- 2 ment of a combination refrigerator and the higher temperature evaporator 8 may be employed to cool the fresh food compartment. The higher temperature evaporator 8 is supplied with refrigerant from the header 3. Liquid refrigerant is normally present within the header 3 at some level as indicated at .9. A conduit It for supplying liquid refrigerant to the bottom of the tubing which forms the evaporator 8 is connected in communication with the header 3 below the normal level of liquid refrigerant within the header. Refrigerant vaporizing within the evaporator 3 is returned to the header 3 through the conduit ii I, this conduit being connected to the header in communication therewith above the level of liquid refrigerant in the leader. Thus, the higher temperature evaporator 8 is connected in a closed circuit to the header 3, liquid refrigerant bein supplied to .the evaporator through the conduit Ill and vaporized refrigerant being returned to the header through the conduit H. The suction line 1 through which vaporized refrigerant is returned to the condensing unit I through the header 3 is, of course, connected in communication with the header above the level of liquid refrigerant therein.

In order to control the flow ofrefrigerant to the higher temperature evaporator 8 so as to maintain the temperature of the fresh food compartment within predetermined limits a solenoid valve I2 is placed in the conduit it through which liquid refrigerant is supplied to the evaporator 8. The openin and closing of the valve I2 is controlled by a switch is actuated by a bellows i l. The expansion and contraction of the bellows to move the switch is governed by a temperature-responsive bulb l5 which is disposed on the evaporator 8 and communicates through a tube It with the bellows. The solenoid valve is energized from power lines I'l, I8 through a circuit including lines til and flll. As th bellows expands because of increase in temperature of the evaporator 8 the circuit through thesolenoid valve is closed by engagement of the-contacts 2| by the switch It. The solenoid valve [2 is normally closed. As the temperature of the evaporator 8 reaches ,a predetermined maximum, the expansion of the bellows Mcloses the circuit of the solenoid valve, moving this valve to its open position. Liquid refrigerant is then supplied to the evaporator .8 through the conduit {0 until the temperature hasbeen reducedto a predetermined .rninimum. .The resultant contraction of the bellows It then opens ate the switch is controlled by a temperatureresponsive bulb 21 which is connected by a tube 28 in communication with the bellows 26. The bulb 21 is placed in heat exchange relationship with the header 3. To obtain rapid response to refrigeration requirements of the higher temperature evaporator, the bulb is located at a point above the level of liquid refrigerant therein. When the temperature of the header 3 increases to a predetermined maximum, the expansion of the bellows 26 closes the circuit to the condensing unit starting the operation of the condensing unit. The unit continues to operate until the temperature of the header 3 reaches a predetermined minimum at which point the contraction of the bellows interrupts the circuit of the condensing unit.

In constructing the evaporators the low temperature evaporator 2 is preferably made with a minimum of tubing of small diameter so that the liquid required to fill this evaporator is not excessive. On the other hand, the higher temperature evaporator should have large tubing in order to minimize the pressure drop therethrough and it should be made as long as possible consistent with good circulation so that this evaporator may be large and have a high rate of heat transfer to the fresh food compartment.

When the valve I2 is closed, the fresh food evaporator. 8 is filled with vaporized refrigerant. This evaporator, therefore, warms up relatively quickly during this period and it may be operated on a defrosting cycle so as to defrost during the time the valve I2 is closed. When the valve I2 is open, liquid refrigerant flows into the evaporator 8, and vaporizes in this evaporator. This results in an increase in pressure in the header 3 and condensation of vaporized refrigerant in the header. During this condensation, the latent heat of vaporization of the refrigerant is given up to the header, warming the header. The increase in pressure in the header also forces liquid refrigerant into the frozen food evaporator 2.

It will be noted that the bulb 21 is arranged in heat exchange relationship with the header 3. To obtain rapid response to refrigeration requirements of the higher temperature evaporator, the bulb 2'! is placed at a point above the level of liquid refrigerant in this header. Thus, when the higher temperature evaporator 8 requires refrigeration, the vaporized refrigerant from the higher temperature evaporator, warming the header as explained above, has a rapid effect on the bulb 21 causing the condensing unit to start more quickly than were the bulb disposed on the surface of the evaporator 2. Under this latter condition, the higher temperature evaporator 8 might require refrigeration at a time when the low temperature evaporator 2 was completely satisfied and, hence, there might be a substantial delay in the starting of the condensing unit. By arranging the bulb on the header 3, the response of the condensing. unit when the higher temper- 4 ature evaporator 8 requires refrigeration is hastened.

The effect of arranging the bulb on the header is illustrated in the graph shown in Fig. 4. The control may be arranged, for example, so that the condensing unit is started whenever the header, as indicated by the bulb 21, reaches 5 F. and the condensing unit may be stopped when the header temperature reaches -4 F. Under the conditions illustrated in Fig. 4, the valve I2 opens because of a rise in the temperature evaporator 8 to a predetermined maximum at a point indicated at a on the curve of temperature of the higher temperature evaporator. This corresponds to the point a on the curve of temperature of the header. The header temperature rises rapidly under the influence of vaporized refrigerant from the higher temperature evaporator and, in a very short time, reaches 5 as indicated at b in Fig. 3, at which time the condensing unit is started. After the requirements of the higher temperature evaporator have been satisfied, the valve l2 closes at a point indicated at c on the curve of the temperature of the higher temperature evaporator. The header temperature drops sharply and ultimately reaches a temperature of -4 F., as indicated at d in Fig. 4, at which time the condensing unit is stopped. It can be seen by referring to Fig. 4 that the arranging of the bulb on the header 3 effects a prompt starting of the condensing unit when the valve l2 in the refrigerant circuit of the higher temperature evaporator opens, even though the'low temperature evaporator 2 may not require refrigeration at that time.

For comparison, a graph showing the temperatures of the low temperature evaporator, the higher temperature evaporator and the header is shown in Fig. 5 to illustrate the various temperature changes under conditions where the valve l2 opens to supply refrigerant to the higher temperature evaporator at a time when the condensing unit is already in operation. The points at which the condensing unit starts and stops and at which the valve I2 opens and closes have been indicated on the graph in Fig. 5.

In the form of invention illustrated in Fig. 1, the flow of refrigerant through the evaporator 8 is effected by the static head in the conduit l9. In order to secure a greater pressure differential and thereby to facilitate the flow of refrigerant and the returnof oil, conduit ll may be made continuous with conduit 1 so as to provide a 'path from the evaporator 8 through the conduit ll directly to the suction line I. This modification is shown in Fig. 2. In this modified form of invention, one or more openings 29 are provided in the portion 30 of the conduit which extends through the header 3. Vaporized refrigerant collecting in the header from the low temperature evaporator 2 is withdrawn through the openings 29 into the suction line 1.

Still another modified form of my invention is illustrated in Fig. 3. In this modified form, the open ends 3| and 32 of conduits l and (respectively, are positioned within the header 3 in line with each other and in proximity to each other. The space 33 between the ends of the conduits l and H is merely sufiicient to pass vaporized refrigerant from the frozen food edvaporator into the suction line I with a nominal rop.

While I have shown and described specific forms of my invention, I do not intend my invention to be limited to the particular construction shown and described and I intend, by the appended claims, to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A refrigerating system comprising a condensing unit, a low temperature evaporator and a header connected in closed series refrigerant circuit, said header having liquid refrigerant therein, a higher temperature evaporator, a first conduit for supplying liquid refrigerant from said header to said higher temperature evaporator, said conduit being connected to said header below the level of liquid refrigerant therein, a second conduit for conducting vaporized refrigerant from said higher temperature evaporator to said header, said second conduit communicating with said header above the level of liquid refrigerant therein, means for withdrawing vaporized refrigerant from said header and returning it to said condensing unit, a valve in said first conduit for controlling flow of refrigerant to said higher temperature evaporator, means dependent on the temperature of higher temperature evaporator for controlling said valve, and a temperature-responsive element positioned on said header above the level of liquid refrigerant therein for controlling the operation of said condensing unit.

2. A refrigerating system comprising a condensing unit, a low temperature evaporator and a header connected in closed series refrigerant circuit, said header having liquid refrigerant therein, a higher temperature evaporator, a first conduit for supplying liquid refrigerant from said header to said higher temperature evaporator, said conduit being connected to said header below the level of liquid refrigerant therein, a second conduit for conducting vaporized refrigerant from said higher temperature evaporator to said header, said second conduit communicating with said header above the level of liquid refrigerant therein, means for withdrawing vaporized refrigerant from said header and returning it to said condensing unit, means for controlling flow of refrigerant to said higher temperature evaporator, and a temperature-responsive element positioned on said header above the level of liquid refrigerant therein for controlling the operation of said condensing unit.

3. A refrigerating system comprising a condensing unit, a low temperature evaporator and a header connected in closed series refrigerant circuit, said header having liquid refrigerant therein, a higher temperature evaporator, a first conduit for supplying liquid refrigerant from said header to said higher temperature evaporator, said conduit being connected to said header and opening into said header below the level of liquid refrigerant therein, a second conduit for conducting vaporized refrigerant from said higher temperature evaporator to said header, said second conduit being connected to said header and opening into said header above the level of liquid refrigerant therein, means for withdrawing vaporized refrigerant from said header and returning it to said condensing unit, means in said first conduit dependent on a condition of said higher temperature evaporator for controlling flow of refrigerant to said higher temperature evaporator, and a temperature-responsive element positioned on said header above the level of liquid refrigerant therein for controlling the operation of said condensing unit.

4. A refrigerating system comprising a condensing unit, a low temperature evaporator and a header connected in closed series refrigerant circuit, said header having liquid refrigerant therein, a higher temperature evaporator, a conduit for supplying liquid refrigerant from said header to said higher temperature evaporator, said conduit being connected to said header below the level of liquid refrigerant therein, means for withdrawing vaporized refrigerant from said header and from said second evaporator, said means including a conduit connected to said higher temperature evaporator and passing through said header above the level of liquid refrigerant therein, the portion of said conduit within said header having at least one opening therein for receiving vaporized refrigerant from said header, means for controlling flow of refrigerant to said higher temperature evaporator, and a temperature-responsive element positioned on said header for controlling the operation of said condensing unit.

5. A refrigerating system comprising a condensing unit, a low temperature evaporator and a header connected in closed series refrigerant circuit, said header having liquid refrigerant therein, a higher temperature evaporator, a conduit for supplying liquid refrigerant from said header to said higher temperature evaporator, said conduit being connected to said header below the level of liquid refrigerant therein, means including a conduit for withdrawing vaporized refrigerant from said header, a conduit for conducting vaporized refrigerant from said higher temperature evaporator to said header, said conduits having open ends within said header positioned in line with and in proximity to each other, said open ends being positioned above the level of liquid refrigerant in said header, means for controlling flow of refrigerant to said higher temperature evaporator, and a temperature-responsive element positioned on said header for controlling the operation of said condensing unit.

CHARLES S. GRIMSHAW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,523,112 Fitzgerald Jan. 13, 1925 1,949,676 Candor Mar. 6, 1934 1,955,087 Philipp Apr. 17, 1934 2,030,676 Atchison Feb. 11, 1936 2,133,949 Buchanan Oct. 25, 1938 2,198,328 Brown Apr. 23, 1940 2,240,284 Buchanan Apr. 29, 1941 

